Flooding rains that killed at least 15 people when they slammed into the fertile and industrious heartland of northeastern Italy in mid-May were at least partly fueled by global warming, and scientists say they fit the trend of intensifying extremes on both the wet and dry sides of the global water cycle.

Warming oceans, which hold more than 90 percent of the heat trapped by greenhouse gases, are driving part of the cycle, said Fred Hattermann, leader of a research team working on hydroclimatic risks at the Potsdam Institute for Climate Impact Research. 

He said the May floods in Italy’s Emilia-Romagna region show how regional extremes are linked and can intensify each other. In the weeks preceding the intense rainstorms, the western Mediterranean region was locked in a very early season heatwave and drought, which warmed up the adjacent Mediterranean, steaming moisture off its surface. Starting in May, that moisture fed a series of storms spinning across northern Italy. Farther east, after the storms picked up more moisture from the Adriatic, Croatia was also hit hard by flooding. 

And the drought preceding the intense rainstorms also intensified the flooding, he said, because the long dry spell and record heat last summer partially baked the soil, hindering its ability to absorb the deluge.

Several recent attribution studies have shown how global warming escalated the likelihood of specific extreme rainfall and flooding events, including the 2021 storms and floods in western Europe, primarily Germany and parts of Belgium, that killed more than 200 people. Hattermann said there is research showing an increasing predominance of certain types of weather patterns, marked by trapped waves in upper-level winds, that can lead to both dry and wet extremes.

In a post showing the dramatic geographic scope of the flooding, NASA said the frequency of flash flooding has increased in the region the past 20 years, citing research by Italian hydrologist Paolo Billi. In addition to storms supercharged by global warming, land use changes, including urbanization, agriculture and river channeling, have also affected the intensity of floods, the post noted. 

By the middle of May, the rains had intensified and spread more widely across the Emilia-Romagna, a wedge of Italy about the size of New Hampshire tucked into the top of the backside of the Italian boot. The region is an industrial center with car and ceramics manufacturing, as well as a breadbasket known for Parmigiano Reggiano and Grana Padano cheeses, balsamic vinegar and Parma ham. And the flooding also threatens priceless cultural treasures in several historically important towns.

The region includes part of the watershed of Italy’s largest and most important river—the Po—which is fed by tributaries from the Apennine Mountains, where a drought of snow prevailed last winter. 

But spring rains dropped six months worth of rainfall—up to 8 inches—in 36 hours at some measuring stations in the region, and 23 rivers overflowed. At least 5,000 people were displaced and the floods caused at least €5 billion ($5.8 billion) in damage to private property and infrastructure, according to a May 22 flood bulletin from Copernicus, the European Climate Service. 

And as observations and climate model projections show, it’s bound to happen again sooner rather than later, said Sonia Seneviratne, a climate extremes expert at the ETH Zürich and a lead author of the recent 6th Assessment Report from Intergovernmental Panel on Climate Change. 

That report states that “‘the frequency and intensity of heavy precipitation events have likely increased at the global scale over a majority of land regions with good observational coverage,’” she said. “It also concludes that ‘human influence, in particular greenhouse gas emissions, is likely the main driver of the observed global-scale intensification of heavy precipitation over land regions.’”

The global signal of more intense downpours is not as clear regionally in the Mediterranean as on a global level, but, she said, “We expect this region to show a substantial signal at 2 degrees Celsius of global warming. Thus, the recent event in Emilia Romagna is consistent with what we expect with increasing human-induced climate change.”

Impacts Will Outrace Adaptations Unless CO2 Emissions Stop

Notwithstanding the ongoing flooding in Italy, drying—scientifically linked to global warming by shifts in hemisphere-spanning wind patterns—may be the bigger climate threat in the long run. 

“The Mediterranean region is particularly strongly affected by increasing drought conditions,” Seniveratne said. “There is a clear attributable trend towards increased droughts in the region. But this is not inconsistent with an increase in heavy precipitation as well.” Warmer air dries the soil but when the atmosphere is saturated during wet periods, “the available moisture for short-term rainfall events is higher,” she added.

Robert Vautard, director of the Institut Pierre Simon Laplace climate research center in Paris, affirmed that the Mediterranean, as well as Western Europe and the United States’ Southwest, stand out globally as regions where the global warming fingerprint on drought is unmistakable, which he said has been well documented by the IPCC.

“These are the two regions for which we have confidence in a long-term drought signal attributable to climate change’” he said. “So, when the general trend is drying, you can do whatever you want, you will have less water.” 

Even while cleaning out waist-deep mud after the Emilia-Romagna floods, it’s time to start thinking about “finding more durable, more sustainable ways” of using water in the long-term, he added. 

Restoring natural ecosystems connected to rivers, especially wetlands and riverside forests, has been scientifically shown to buffer the impacts of floods, and also to help preserve river flows during dry times. The World Bank calculates that, in some cases, investing in resilient ecosystems is by far the most cost-effective way to buffer rivers and water supplies from global warming impacts, with a return of $7 to $30 for every $1 invested. The World Bank last week issued a report on the benefits and costs of such nature-based climate solutions.

Even areas that haven’t faced water shortages in the past couple of decades need to start thinking ahead and acting, primarily by implementing watershed-based management plans that incorporate the best available climate projections. Several major urban centers have come perilously close to running out of water recently, including Cape Town in 2018, where an attribution study found that global warming tripled the chance for extreme drought. 

Most recently the water crisis in Uruguay has led to social unrest and is reportedly forcing the government to subsidize water bottling corporations to ensure emergency supplies, with less than a month’s worth of water left in Montevideo’s supply system.

Seneviratne agreed that more adaptation is needed, but the focus should be on stopping greenhouse gas emissions as soon as possible, otherwise the impacts will outpace our ability to adapt—which is already happening in some cases. 

“Heavy precipitation events will keep on becoming more intense with increasing fossil fuel use and CO2 emissions,” she said. “For this reason, bringing emissions to zero is absolutely essential to stabilize the climate conditions.”